A polarizing plate has been typically used in a structure in which a protective film is laminated on one surface or both surfaces of a polarizer using an adhesive, in which the polarizer is formed of a polyvinyl alcohol (hereinafter, referred to as ‘PVA’)-based resin dyed with a dichroic dye or iodine. According to the related art, triacetyl cellulose (TAC)-based films have been usually used as protective films for a polarizing plate, but such TAC films have problems in that the films may be easily deformed under high temperature and high humidity environments. Accordingly, protective films formed of various materials, which are capable of being substituted for such TAC films, have been currently developed, and for example, methods of using polyethylene terephthalate (PET), cycloolefin polymer (COP), acrylic films, and the like alone or in combination have been proposed. Among them, acrylic films are advantageous in view of excellent optical properties and durability, and low costs, and thus are getting special attention.
However, since the surface of the films has non-polar characteristics, adhesive strength is not sufficiently secured when using a water-based adhesive which has been used for attaching a protective film to a polarizer in the related art. Further, since a polyvinyl alcohol-based resin, which is a main component, is an aqueous polymer in a polyvinyl alcohol-based adhesive usually used as the water-based adhesive, peeling often occurs at an interface between the polarizer and the protective film under humidity conditions. Methods of using a non-water based adhesive have been proposed in order to solve these problems, but an acrylic film has high surface frictional force and poor resistance to an organic solvent, and thus, it is difficult to coat an adhesive layer, and when an adhesive including an organic solvent is used, problems in that the surface of the film is damaged and the like occur.
In general, one surface of a polarizer protective film may include various functional coating layers such as a reflection prevention layer and a hard coating layer on an opposite surface to a surface onto which a polarizer is attached, for the purpose of preventing reflection, improving durability, preventing scratches, improving visibility, and the like, and these functional coating layers are generally formed by a method of applying a coating composition including a base resin, a solvent, an additive, and the like onto a protective film, and then curing the coating composition. However, the acrylic film has poor solvent resistance, so that there may occur a problem in that the functional coating layer is not coated well, or the surface of the film is melted and damaged when the functional coating layer is formed, and the like.
Since the acrylic film has higher surface frictional force than films formed of other materials, there are problems in that slip properties are poor during the winding of the film, so that the workability deteriorates, and there occurs a blocking phenomenon in which the film surfaces are adhered to each other after winding the film.
Therefore, there is a need for developing an optical film having excellent water resistance and solvent resistance while satisfying slip properties and not hindering transparency.